An ADvanced Super Dimension Switch technology (ADS) is a wide-viewing angle technology, which has been proposed for liquid crystal televisions and tabletop displays of large-size and high-resolution in the liquid crystal field at present. Because it possesses advantages of wide viewing angle, high aperture ratio, low power consumption, high luminance, and so on, its application is becoming more and more widespread. In this technology, a multi-dimensional electric field is formed by an electric field produced at edges of slit electrodes on the same plane and an electric field produced between a slit electrode layer and a plate-like electrode layer, so as to allow liquid crystal molecules at all orientations in a liquid crystal cell, which are located directly above the electrode and between the slit electrodes, to be rotated, thereby enhancing the work efficiency of liquid crystals and increasing transmissive efficiency. The Advanced Super Dimensional Switch technology can improve the picture quality of TFT products, and has advantages of high resolution, high transmittance, low power consumption, wide viewing angle, high aperture ratio, low chromatic aberration, and push Mura-free, etc.
In a current process for manufacturing an array substrate of a thin film transistor liquid crystal display (TFT-LCD), a plurality of photolithography procedures are used to perform patterning for thin film layers so as to form a plurality of thin film (pattern) layers. For ensuring exactness of each of the photolithography procedures, it is necessary to make sure the alignment accuracy among the plurality of photolithography procedures by space imaging overlay inspections. Generally, in an overlay inspection, an overlay mark on a photomask is used to form an overlay mark pattern in the thin film layer formed by photolithography, and by means of checking a shift between overlay mark patterns on adjacent thin film layers, alignment condition between two photolithograph procedures can be effectively detected. Thus, precise alignment of the overlay mark patterns on two adjacent thin film layers is the key to ensure accuracy of the overlay inspection.
With a current process for manufacturing an array substrate of an ADS mode TFT-LCD as an example, a layer of indium tin oxides (ITO) conductive film is formed on a glass substrate in a first photolithography, and a layer of metal gate thin film is further formed on a surface of the layer of the ITO thin film in a second photolithography. However, the ITO thin film is a transparent conductive thin film, and before an overlay inspection between the gate thin film layer and the ITO thin film layer is conducted, photoresist on the surface of the ITO thin film layer (photoresist is usually non-transparent, and an overlay mark pattern on it is relatively clear) has already been removed, and therefore, when the overlay inspection is conducted between the gate thin film layer and the ITO thin film layer, transparency of the ITO thin film layer often results in such a case that an overlay mark pattern on the ITO thin film layer cannot be positioned accurately, and accordingly time consumption for the overlay inspection is longer.